As a conventional headset for performing simultaneous two-way communication or alternate two-way communication under high noise conditions as described above, there is often used a headset in which a pair of hermetically-sealed bowl-shaped housings 31 each having an annular pad 32 attached to the rim of an opening portion are connected together through a headband 33, an acoustic speaker 34 is arranged in at least one of the housings 31, and a close-talking boom microphone 35 that extends to the mouth is provided in one of the housings 31 (for example, FIG. 5 and Japanese Utility Model Laid-Open No. 62-186585).
Some headsets employ a bone conduction microphone 36 instead of the boom microphone 35. In this case, the bone conduction microphone 36 is embedded in a projecting portion 35 for mounting a bone conduction microphone that is formed by extending a portion of the housing 31 (see FIG. 6).
However, the headset of the type using the boom microphone 35 has a disadvantage that its performance is variable depending on a position where the boom microphone 35 is set and the headset cannot be used in an environment in which an operator needs to wear a mask. Also, the headset of the type using the bone conduction microphone 36 has a disadvantage that external noise is easily mixed since the projecting portion 35 for mounting a bone conduction microphone is located outside the annular pad 32 having sound insulating properties.    Patent Document 1: Japanese Utility Model Laid-Open No. 62-186585